The present invention relates to a magnetic head, a method of manufacturing the magnetic head, a head suspension assembly and a magnetic disk apparatus.
With the trend to a larger capacity and a smaller size of hard disk drives (HDD), heads are required to have a higher sensitivity and a larger output. To meet these requirements, strenuous efforts have been made to improve the characteristics of GMR heads (Giant Magneto-Resistive Head) currently available on the market. On the other hand, intense development is under way for a tunnel magneto-resistive head (TMR head) which can be expected to have a resistance changing ratio twice or more higher than the GMR head.
Generally, the GMR head differs from the TMR head in the head structure due to a difference in a direction in which a sense current is fed. A head structure adapted to feed a sense current in parallel with a film surface, as in a general GMR head, is referred to as a CIP (Current In Plane) structure, while a head structure adapted to feed a sense current perpendicularly to a film surface, as in the TMR head, is referred to as a CPP (Current Perpendicular to Plane) structure. Since the CPP structure can use a magnetic shield itself as an electrode, it is essentially free from short-circuiting between the magnetic shield and a device (defective insulation) which is a serious problem in reducing a lead gap in the CIP structure. For this reason, the CPP structure is significantly advantageous in providing a higher recording density.
Other than the TMR head, also known as a head in CPP structure is, for example, a CPP-GMR head which has the CPP structure, though a spin valve film (including a specular type and dual spin valve type magnetic multilayer film) is used for a magneto-resistive device (see JP-A-2003-60262 corresponding to U.S. patent application Publication No. 2003/0039080).
Some magnetic heads comprise a magneto-resistive device which has a magneto-resistive layer including an oxide layer. For example, a TMR head employs an oxide layer made of Al2O3 or the like for a tunnel barrier layer which forms a part of a magneto-resistive layer (see JP-A-2003-27258 and JP-A-2003-60262). A CPP-GMR head may include an oxide layer such as a thin insulating layer which acts as a current path control layer partially having a metal region within an insulating region formed between two layers in order to effectively reduce the area of the path through which a sense current flows (see JP-A-2003-60262).
In a magnetic head, since the end face of the magneto-resistive device appears on a side facing to a magnetic recording medium, i.e., an air bearing surface (hereinafter abbreviated as “ABS”), it is necessary to prevent corrosion of end faces of metal layers which make up the magneto-resistive device. It is also necessary to enhance the slidability of the ABS for avoiding head crush, damages to a magnetic recording medium, and the like. Particularly, in a magnetic disk apparatus which employs a CSS (contact start stop) method, the ABS of a magnetic head comes into contact with the surface of a disk at the start and end of driving, so that the ABS is required to have a high slidability (low friction). To meet the requirements, conventionally, the ABS is formed with a protection film for increasing the aforementioned corrosion resistance and slidability, so that the end face of the magneto-resistive device on the ABS side is covered with the protection film. Generally, the protection film is made of a DLC (Diamond-Like-Carbon) film (see JP-A-2003-27258, JP-A-8-297813, JP-A-9-231539, JP-A-9-128708, JP-A-7-6340 corresponding to U.S. Pat. No. 5,930,077, and JP-A-2003-60262 corresponding to U.S. patent application Publication No. 2003/0039080).
JP-A-2003-27258 and JP-A-8-297813 disclose a silicon film or a silicon oxide film used for an underlying layer of a DLC film, i.e., a protection film, in order to act as an adhesive layer. JP-A-9-231539 and JP-A-9-128708 disclose a silicon film used for an underlying layer of a DLC film, i.e., a protection film, in order to act as an adhesive layer. JP-A-7-6340 in turn discloses that an underlying layer (referred to as an “intermediate layer” in JP-A-7-6340) of a DLC film (i.e., a protection film) is formed of a layer made of at least one element selected from the group consisting of hard carbon, silicon, boron, titanium and aluminum, and carbide, nitride and oxide of silicon, boron, titanium, or aluminum. Further, JP-A-7-6340 discloses a sputtering method used for forming the underlying layer of the DLC film, and also discloses, with respect to a sputtering target and a sputtering gas, that there are (i) a method which uses a plate of the same element as the film to be formed, or a plate of a compound including the same element and an argon gas, and (ii) a method which uses a plate of an element which is included in the film and a hydrocarbon gas, an ammonia gas or an oxygen gas, when the underlying layer to be formed is made of a carbide, a nitride or an oxide, and that any of the two method may be used for the intended purpose.
The result of an investigation made by the present inventors has revealed that in a magnetic head which comprises a magneto-resistive device having a magneto-resistive layer including an oxide layer, for example, such as a TMR head, when an underlying layer of a protection layer formed on ABS is made, for example, of a silicon film, the resistance of the magneto-resistive device relatively largely varies before and after the magnetic head is left in a high temperature environment, thus exhibiting low stability of the characteristics of the magnetic head with respect to a high temperature environment.